Press forging die

ABSTRACT

A hot work implement, such as a press forging die and analogous products, which has excellent secondary hardening and temper resistance, toughness, wear resistance, and machinability properties as contrasted to products currently on the market, said implement being economically competitive with existing implements and having the following nominal composition by weight per cent in its broadest embodiment:   D R A W I N G

[451 Oct. 14, 1975 PRESS FORGING DIE [75] Inventors: George M. Waid, Williamsfield; Robert T. Ault, Shaker Heights, both of Ohio [73] Assignee: A. Fink] & Sons Company, Chicago,

Ill.

22 Filed: Oct. 10,1973 [211 App]. N0.: 405,165

[52] US. Cl. 148/38; 75/124; 75/128 V; 75/128 W [51] Int. C1. C22C 38/44; C22C 38/46 [58] Field of Search 75/124, 128 W, 128 V; 148/38 [56] References Cited UNITED STATES PATENTS 2,763,544 9/1956 Wagner 75/124 3,291,655 12/1966 Gill 75/124 3,316,084 4/1967 Manganello 75/124 3,368,887 2/1968 Enis 75/124 3,619,179 11/1971 Malagari. 75/124 3,645,723 2/1972 Riedel 75/124 OTHER PUBLICATIONS Tool Steels", Roberts et al., third edition, ASM-l962 pp. 232235,550-56l.

Primary ExaminerL. Dewayne Rutledge Assistant Examiner-Arthur J. Steiner ABSTRACT A hot work implement, such as a press forging die and analogous products, which has excellent secondary hardening and temper resistance, toughness, wear resistance, and machinability properties as contrasted to products currently on the market, said implement being economically competitive with existing implements and having the following nominal composition by weight per cent in its broadest embodiment:

C .15 .35 Mn .50 .90 Si .15 .40 Ni 1.0 3.5 Cr .5 4.5 Mo .5 3.0 V .2 1.0 A1 .01 .07

10 Claims, 2 Drawing Figures PRESS FORGING DIE C Mn Si Broad .15-.35 .50-.90 .15-.40 Preferred .15-.25 .55-.80 .15-.40 Specific .17-.22 .5S -.80 .20-.3S

sistance and improved machinability as contrasted to press dies currently available.

BACKGROUND OF THE INVENTION There is a trend in the drop forging industry to change over from drop hammers to forging presses. The reasons for this trend include obtaining improved yields, faster operation at lower cost, and use of a lower labor grade. Other factors such as the environmental consideration of reduced noise levels favor the increased use of press forging.

As those skilled in the art appreciate a workpiece which is press forged is in contact with the die for a longer period of time on the average than a piece which is drop hammer forged. Because of this longer dwell period of contact the dies reach higher temperatures than drop forge dies and accordingly good secondary hardening and temper resistance, that is, resistance to softening at elevated working temperatures, is necessary.

Further more hot metal flow over the die surfaces is present in press forging, due to the long squeeze effect, as contrasted to drop forging. Accordingly good wear resistance at elevated temperatures is essential.

Good impact toughness is essential since press forging dies are subjected to shock loading. If a press die is deficient in impact toughness heat checking readily leads to cracking; when cracking occurs the useful life of the die is ended, since dies which have heat checked and then cracked cannot be redressed or polished.

Further, since a press die is nearly always resunk one or more times during its useful life it is important that it possess good hardenability so the number of pieces that can be expected from the last sinking is as great as from the first.

Since a press die block like any other die block must be machined to form the desired cavity, it is also important that the material be as machinable as possible. This is a difficult requirement to achieve when taken with the foregoing requirements, since attainment of good hot hardness and wear resistance properties aresomewhat incompatible with good machinability.

And finally, the press die must be economically competitive since alternative products are available to the trade.

SUMMARY OF THE INVENTION The invention is a press forging die block which, when subjected to tempering in the range of about 900F to ll50F following austenitizing at about l800F, has excellent secondary hardening and temper resistance, good hot hardness and therefore good wear resistance at the elevated temperatures encountered in press die forging, excellent impact toughness and resistance to heat checking and consequent cracking, and improved machinability as contrasted to existing products, all of said characteristics being achieved at a lower cost than said existing products. The invention further includes a steel especially adapted for use as a press forging die and having the following broad, preferred and specific ranges:

Ni Cr Mo V Al DESCRIPTION OF THE DRAWINGS Several features of the invention are illustrated in the accompanying drawing wherein:

FIG. 1 is a comparison of tempering response curves for a standard steel and the steel of this invention; and

FIG. 2 is a comparison of the influence of tempering temperature on hardness and toughness of a standard steel and the steel of this invention.

DESCRIPTION OF SPECIFIC EMBODIMENT Carbon is necessary to provide the requisite hardness and contributes to the secondary hardening effect and wear resistance. Carbon makes possible the formation of carbides, such as Mo C and V C which produce the secondary hardening effect, and should be balanced with the secondary hardening elements Cr, Mo and V. If substantially more than .35 C is present, the product may be too brittle and if substantially less than .15 C is present the requisite secondary hardening effect may not be achieved. If melting conditions permit the range of .17 to .22 C ensures the presence ofa near optimum amount of C when the other secondary hardening elements are present in the specified ranges.

' Mn contributes to hardenability and controls sulphides. Manganese sulphide is far preferable to ferrous sulphide in a forging steel since manganese sulphide does not cause hot shortness as does ferrous sulphide. If substantially more than the specified amount of Mn is present a refractory reaction during the steelmaking process may occur with a consequent adverse effect on cleanliness. If substantially less than the specified amount of Mn is present surface problems, such as cracking, may be encountered.

Si is important because of its contribution to the steelmaking process including, particularly, serving as a blocking agent.

Ni is essential because of its contribution to'toughness, in particular, and hardenability. It also helps resist heat checking. If substantially more Ni is present than specified the die may be flake sensitive and tend to retain austenite; further, Ni is a relatively expensive element. If substantially less Ni is present than that specitied the requisite toughness may not be achieved. Ni in an amount near the upper end of the range should be present for optimum results.

Cr contributes to secondary hardening and temper resistance, toughness and hardenability. It has been ob served in experiments that steels of the invention containing Cr are characterized by a low C martensitic structure when air cooled, whereas similar steels which lack Cr are characterized by the less desirable low carbon bainitic structure. Substantially greater amounts of C Mn Standard .21 .67

Steel New Steel the broad range, and most preferably near the midpoint of the range.

M is essential because of its contribution to carbide formation and hence hardness throughout a wide temperature range. It is important that a press die or similar product not soften, wear or erode in use, and Mo contributes to these desirable properties. Mo also has a beneficial effect on hardenability. If more than the indicated amount of M0 is present the C would have to be increased and a tendency toward brittleness might develop. If less than the specified amount is present the desired effects'may not be achieved. It is preferred that Mo be present in the lower end of its broad range, and most preferably in an amount of from 1.0 to 1.2%.

V is essential because it provides increased temper resistance and secondary hardening since it is a potent carbide former. Experiments have also indicated that V provides excellent hot hardness properties which indicates greater wear resistance in service as contrasted to similar steels which do not contain V. Although a lower limit of 0.30% has been specified for both the preferred and specific ranges, the improved temper resistance 4 Two -lb. vacuum induction melted ingots were melted to the following compositions:

Si P S Cr M0 V Ni Al .35 .008 .017 nil 3.35 .08 3.15 .022

The ingots were forged to 2- inch square bars and then further reduced to 1% inch square bars with a soaking temperature of 2250F before forging. Hardness tests were then conducted on specimens of each steel after aging for 4 hours at various temperatures in the range of 700F to 1300F, and the results plotted in FIG. 1. By reference to FIG. 1 it will be noted that although the new steel had a slightly less pronounced secondary hardening peak response characteristic than the standard steel, it has substantially improved temper resistance. In this connection it should be noted that the slight decrease in peak hardness of the new steel is more than compensated by the improved temper resistance and toughness properties, the latter of which will be discussed hereafter. Of special note in FIG. 1 is the sustantially improved temper resistance which was achieved with the approximately 6-fold increase in V.

The improved hot hardness properties of the invention are apparent'from Table I, which sets out tests on the aforesaid 1% square bars after austenitizing, air cooling, and aging at about 975F for 4 hours to a common hardness level of about R 46 i 1.

TABLE I BRINELL HOT HARDNESS For 1 100 F test. the spccimcnts from the 900 F test were rc-uscd.

Of particular interest are the BHN values after 100 hours. The 900F hardness values show no significant difference which is to be expected, since this test temperature is below the aging temperature used for these steels. The hardness values of the 1000F and ll0OF test temperatures clearly indicate that the new die steel has superior hot hardness characteristics as compared to the standard steel, thus indicating that the new steel will have greater wear resistance in service.

The outstanding impact toughness of the invention can be appreciated from Table II, which shows Charpy V-notch impact toughness properties determined at F, 212F, and 350F for various tempering tempera-' tures, and FIG. 2.

TABLE ll CHARPY IMPACT TOUGHNESS PROPERTIES AND HARDNESS Tempering Charpy impact Energy, ft-lbs.

Temp (F) (+70 F) (+212 F) (+350 F) Hardness (Rc) Standard 900 21.5 39.1 Steel 950 13.7 21.5 30.2 42.0 1000 8.0 27.0 45.3 1050 4.7 47.3 1100 6.0 11.2 9.7 43.0 1 150 7.7 41.2

New Steel 900 28.5 44.6 950 22.0 34.0 39.7 45.5 1000 28.5 44.2 46.2 1050 30.0 44.8 1100 27.2 39.6 41.5 44.5 1 150 33.0 43.4

Note: CVN values are the average of two tests.

The heat treatment for the standard steel specimens 20 After forging to 9% inch round bars and suitable heat and the new steel specimens was identical with the exception that the standard steel was austenitized at its recommended temperature of 1850F while the new steel was austenitized at 1800F, this latter temperature having been established as sufficient to ensure complete solution of all alloy carbides.

From Table II it will be noted that the toughness of the new steel was significantly greater than the toughness of the standard steel at all tempering temperatures and all test temperatures. 1

From FIG. 2, which is based on the data of Table II, the superior impact toughness of the new steel is charted. Particular attention is directed to the 1100F tempering temperature since the hardness of the standard steel and new steel specimens was approximately equal at that temperature. The superiority of the new steel is clearly apparent at this point wherein all variables are equal within the limits of experimental error.

Further experimentation has indicated that an aluminum-killed fine grain melting practice is a significant factor in the improved impact toughness of the new steel as compared to the standard steel, both as a function of tempering temperature and austenitizing temperature.

.lominy tests have indicated that the new steel has equal, if not better, hardenability than the standard steel. A comparison of micro-structures of the two types of steels revealed that the new steel has a low carbon martinsitic structure, at least when air cooled in /2 inch thick sections, whereas the standard steel exhibits a less desirable, low carbon bainitic structure. Good hardenability is desired in this product since the number of pieces made from the second and each further sinking should be as great, if possible, as the number of pieces obtained from the initial sinking.

In a further test, a 65-ton heat of steel was melted and the following composition obtained:

treatment which included austenitizing at 1800F for 6-8 hours, air cooling to below 500F, tempering in the range of 1125" F to 1150F, and air cooling, the steel round was split into a pair of upsetter dies which were machined and polished for use in press forging automotive parts. The new steel, which was machined and pol- V ished under the same conditions as the standard steel, machined and polished better than the standard steel. A first set of dies was installed in place ofa set ofdies 30 made from the above mentioned standard steel, and

run under the same conditions to produce the same automotive part as had the standard steel. Said first set of dies yielded over greater production during its useful life than the average production of the standard 5 steel. A second set of dies yielded over greater production than the average production of the standard steel and, when examined, appeared to be in as good a condition as when installed.

In a further test a series of 0.250-inch diameter bar specimens were made up from the above mentioned 65 ton heat, and a series of tensile tests at varying temperatures were carried out. The test results were then compared against average tensile test results derived from a comparative steel having the following nominal compowhich had been tempered to a hardness level in the range of BHN 375-341. Said comparative steel is another steel which has been used for similar applications, and specifically press forging dies. The properties are summarized in the following Table 111. It will be noted that excellent transverse ductility was obtained in addition to good hot strength.

C Mn P S Si Ni Cr Mo V Al TABLE 111 Ultimate Tensile Ultimate Tensile 0.2% Offset Specimen Test Strength, Psi Strength, Psi, Yield Elong.

Designation Temp.. F Invention Steel Comparative Steel Strength. Psi 1n 1 Inch RA TABLE [ll-continued Ultimate Tensile Ultimate Tensile 0.2% Offset Specimen Test Strength. Psi Strength. Psi. Yield Z Elong. Designation Temp., F Invention Steel Comparative Steel Strength. Psi ln 1 Inch 7r RA C. L 800 144.900 142.000 132.200 10.5 32.7 D. T 800 145.200 128.500 8.2 23.3 E. L 1000 118.800 110.000 101.600 11.4 38.5 F. T 1000 119.600 106.700 10.6 26.1 G. L 1100 100.300 89.000 85.600 13.7 48.4 H. T 1100 100.600 85.100 12.9 36.5 1. L 1150 88.700 78.100 15.9 49.2 J. T 1150 92.000 78.600 17.1 37.7 K. L 1200 74.300 59.100 21.1 55.6 L. T 1200 73.800 58.500 18.4 52.7

Longitudinal.

Transverse.

It should be understood that although the invention has been described in terms of a forging press die other a -53 analogous end products and uses are contemplated and I included within the invention including upsetter dies, Ni 1.8 3.2

insert dies, die casting dies, piercers, punches, centrifugal casting dies, dummy blocks for extrusion, pusher v .30- .65

blocks and extrusion dies. Accordingly, whenever the 7 M Fe balance. together w1th non-deleterlous elements. term press forgmg d1e appears 1n the specificauon and claims it should be understood that the above mentioned uses, and other uses which may be described generally as uses in which the hot work implement is subjected to shock loading, metal flow, and prolonged contact with a work piece, are intended.

It will thus be seen that a new press forging die, and a new steel therefor, which has good heat resistance, excellent precipitation hardening properties, good impact toughness and good machinability has been provided. Resistance to heat checking, wear and die spreading are all improved over standard steels whereby the user has available a superior product which can be made available at the same price as standard steels currently on the market.

Although a preferred embodiment of the invention has been herein described it will at once be apparent to those skilled in the art that further specific modifications and variations may be made without departing from the spirit and scope of the invention. Accordingly it is intended that the scope of the invention be limited, not by the scope of the foregoing description, but solely by the scope of the hereafter appended claims when interpreted in light of the pertinent prior art.

We claim:

1. A press forging die block for shaping hot metal work pieces, said press forging die block being austenitized and having a hardness of at least about 40 Re after temper aging at least 4 hours in the range of 900 to I 150F, and a room temperature tensile strength. of at least about 150,000 psi, said press forging die block consisting essentially of C .15 .35 Mn .50 .90 Si .15 .40 Ni 1.0 3.5 Cr .5 4.5 Mo .5 3.0 V .2 1.0 Al .01 .07 Fe balance. together with non-deleterious elements.

2. The press forging die block of claim 1 further characterized in that said die block has the following composition:

3. The press forging die block of claim 2 further characterized in that Vanadium is present in the range of from 0.40 0.65.

4. The press forging die block of claim 1 further characterized in that said die block has the following composition:

Ni 2.85 3. l5

Fe balance. together with non-deleterious elements.

C l5 .35 Mn 50 .90 Si 15 .40 Ni 1 0 3.5 Cr 5 4.5 Mo 5 3.0 V 2 1.0 .Al 01 .07

Fe balance. together with non-deleterious elements.

7. The press forging die of claim 6 further characterized in that said die has the following composition:

C .15 .25 Mn .55 .80 Si .15 .40 Ni 1.8 3.2 Cr 1.5 2.3 Mo .9 1.6 V .30 .65

9 10 -continued -cntinued Fe balance. together with non-deleterious elements. Si .20 .35

Ni 2.85 3.15 Cr L90 2.10

. '7 8. The press forging die of claim 7 further characterv :2 l ized in that Vanadium is present in the range of from Al .02 .05

Fe balance. together with non-deleterious elements. 0.40 0.65.

9. The press forging die of claim 6 further characterized in that said die has the following compositions: The Press f g ng d e f Claim 9 further Characterized in that Vanadium is present in the range of from o 40 0 3 C .17 .22 Mn .s5-.s0 

1. A PRESS FORGING DIE BLOCK FOR SHAPING HOT METAL WORK PIECES, SAID PRESS FORGING DIE BLOCK BEING AUSTENITIZED AND HAVING A HARDNESS OF AT LEAST ABOUT 40 RC AFTER TEMPER AGING AT LEAST 4 HOURS IN THE RANGE OF 900* TO 1150*F, AND A ROOM TEMPERATURE TENSILE STRENGTH OF AT LEAST ABOUT 150,000 PSI, SAID PRESS FORGING DIE BLOCK CONSISTING ESSENTIALLY OF
 2. The press forging die block of claim 1 further characterized in that said die block has the following composition:
 3. The press forging die block of claim 2 further characterized in that Vanadium is present in the range of from 0.40 - 0.65.
 4. The press forging die block of claim 1 further characterized in that said die block has the following composition:
 5. The press forging die block of claim 4 further characterized in that Vanadium is present in the range of from 0.40 - 0.53.
 6. A press forging die for shaping hot metal work pieces, said die being austenitized and having a hardness of at least about 40 Rc after temper aging at least 4 hours in the range of 900* to 1150*F and a room temperature tensile strength of at least about 150,000 psi, said press forging die consisting essentially of
 7. The press forging die of claim 6 further characterized in that said die has the following composition:
 8. The press forging die of claim 7 further characterized in that Vanadium is present in the range of from 0.40 - 0.65.
 9. The press forging die of claim 6 further characterized in that said die has the following compositions:
 10. The press forging die of claim 9 further characterized in that Vanadium is present in the range of from 0.40 - 0.53. 